Automatic starting and protection system for a gas turbine



Oct. 7, 1969 E. G. SMITH 3,470,691

AUTOMATIC STARTING AND PROTECTION'SYSTEM FOR A GAS TURBINE Filed June17, 1968 2 Sheets-Sheet 2 R f .1. I T Q 88 United States Patent3,470,691 AUTOMATIC STARTING AND PROTECTION SYSTEM FOR A GAS TURBINEEmile G. Smith, Bethe], C0nn., assignor to Avco Corporation, Stratford,Conn., a corporation of Delaware Filed June 17, 1968, Ser. No. 737,743Int. Cl. F02g 3/00; F02c 7/26; F16p 7/00 U.S. Cl. 6039.09 6 ClaimsABSTRACT OF THE DISCLOSURE A gas turbine engine having variable powerturbine stator vanes is automatically started by means of a pushbuttonoperated control unit which serves to energize the starter motor and theignition unit. The starter motor and ignition unit are de-energizedafter a successful start is indicated by a compressor speed comparator,or an attempted start is aborted by de-energizing the starter motor andignition unit after a predetermined elapsed time. During operation,automatic protection is provided against a power turbine overspeedcondition by automatically varying the stator vane position, and againstan overtemperature condition by automatically bleeding main fuel.

BACKGROUND OF THE INVENTION In the starting of a gas turbine engine itis necessary for the operator to manipulate several controls overcritical time periods. In starting and operating any gas turbine enginecertain parameters are critical, and in the ordinary system the operatormust carefully monitor his instruments to make certain that no damagingconditions exist. The particular gas turbine engine, in which thepresent invention was reduced to practice, utilized a free power turbinewith variable power turbine stator vanes and a main fuel bleed valve.The present invention provides automatic monitoring and controlling ofthese devices and, in addition, provides means for automaticallyshutting down the starting procedure after a successful start, oraborting an unsuccessful start after a predetermined elapsed time.

The invention provides: a high pressure compressor speed (N pick-up forproviding a pulse train whose pulse repetition rate is proportional tocompressor speed; a power turbine speed (N pick-up for developing apulse train having a repetition rate proportional to power turbinespeed; a thermocouple harness for sensing engine gas temperature to thepower turbine section which is used to prevent an overtemperaturecondition; and a timer for developing output pulses after apredetermined period of elapsed time if the engine has not yet started.

In the starting cycle, the operator depresses a starting button whichserves to energize a starting relay, closing the circuits to theignition unit and to the starter solenoid, and thereby to the startermotor. If the engine does not start, i.e., attain idle speed, within apredetermined time, the output from a delay timer serves to de-energizethe starting relay, opening the circuits to the starter motor and theignition unit and notifies the operator to abort the starting attempt.If a successful start is accomplished prior to the completion of thedelay time, the output from the N comparator upon attaining apredetermined compressor speed, de-energizes the starting relay andthereby the starting accessories. After a successful start is made,operation is monitored by the power turbine, N speed pick-up and by thethermocouple harness. If the free power turbine speed exceeds apredetermined level, output pulses generated by the N comparator areused to control the stator vanes so as to slow the turbine down. In theevent an overtemperature condition is sensed by the temperaturecomparator, an output is generated by the overtemperature comparator,and this serves to open the main fuel bleed valve which reduces theamount of fuel supplied to the combustion chamber and hence reduceoperating temperatures.

THE DRAWINGS FIGURE 1 is a block diagram showing the overallconfiguration of the system while FIGURES 2 and 3 are schematics of theparticular circuits utilized within the system.

DESCRIPTION OF THE INVENTION The overall system includes a starter motor10 energized by means of a battery 12 through the contacts 14 of astarter solenoid 16, a starting relay 24, and through a master powerswitch S1 and transmission mode switch S2. In addition the systemincludes an ignition unit 18 which functions to energize the spark plugsin the engine when connected to the battery 12. The starter solenoid 16and the ignition unit 18 are each energized through the contacts 20 and22 of a starting relay 24. The starting relay 24 is in turn energized byconnecting the battery 12 through a transmission mode switch 52, whichis closed when the engine transmission is in neutral, and through apushbutton momentary start switch S3. Closing of the master power switchS1 also applies the battery 12 to a voltage regulator 25, the regulatedvoltage output of which appears at a terminal R. The regulated voltageappearing at the terminal R supplies the power for several subsystemswithin the system. For purposes of clarity, the connections from thevoltage regulator 25 to the various circuits have been omitted, it beingunderstood that all of the terminals R are interconnected.

With switches S1 and S2 closed, the momentary closing of the startingswitch S3 applies the voltage from the battery 12 to an ignition andstarter power control circuit 26. This causes the energization of thestarting relay 24 and the closing of the contacts 20 and 22. When thecontacts 20 are closed, the starter solenoid 16 is energized, causingthe contacts 14 to be closed and energizing the starter motor 10. Whenthe contacts 22 are closed, the ignition unit is energized and functionsto ignite the engine fuel.

The compressor speed N pick-up 28 is conventional and in a practicalcase may comprise a magnetic device producing pulses of a repetitionrate proportional to the speed of the high pressure compressor. Theoutput pulses from the N pick-up 28 are analyzed by an N speedcomparator circuit 30 which serves to produce a series of output pulseswhen the speed of the high pressure compressor exceeds a predeterminedlevel. In a successful start this will occur before output pulses aredeveloped by a delay timer 32 and, when applied to the ignition andstarter power control circuit 26, will serve to de-energize the startingrelay 24 and open the circuits to the starter solenoid 16 and theignition unit 18.

In the event that the N comparator does not develop output pulses priorto the expiration of a predetermined time due to a failure to start, anoutput is developed from the delay timer 32 and is applied to theignition and starter power control circuit 26. This also serves todeenergize the starting relay 24, thereby disconnecting the startersolenoid 16 and ignition unit 18.. However, since a start has not beenaccomplished in this case, the attempt is aborted by this reaction andby ordering the operator to abort this attempt.

Therefore, during starting the ignition and starter power controlcircuit 26 can be supplied with pulses from two sources, the Ncomparator 30 or the delay timer 32. If supplied from the N comparator30 through line 31 prior to the application of a pulse from the delaytimer 32 through line 33, the engine has started and operation of thestarter motor and the ignition unit 18 are no longer required.Therefore, the starting relay 24 is deenergized and the delay timerdeactivated through line 35. However, if the delay timer operates beforethe compressor has reached the desired speed, the starter motor 10 andignition 18 are turned off, but in this case the engine is not running,and the starting attempt is aborted.

In the event of any malfunction within the ignition and starter powercontrol 26 or elsewhere in the starting power cycle, the operator canmanually override the automatic system by means of depressing the startswitch a second time. This will deenergize the automatic system and hemay control the engine with a manual starter motor switch S4 and amanual ignition switch S5. These connect the battery directly to thestarter solenoid 16 and the ignition unit 18 and must, of course, bemonitored by the operator.

The battery 12 is also connected through switch S1 via a line 36 to avariable power turbine stator vane solenoid 38 and via a line 40 to amain fuel bleed solenoid 42. The circuit to ground for the stator vanesolenoid 38 is completed through a line 44 and a stator vane powercontrol circuit 46. Similarly, the circuit to ground for the main fuelbleed solenoid 42 is completed through a line 48 and a main fuel bleedcontrol circuit 50.

Each of the connections to ground through the control circuits 46 and 50are normally open, and therefore the solenoids 38 and 42 are normallyde-energized. The power turbine stator vane control circuit 46 completesthe connection of the solenoid 38 to ground when an output is developedfrom the N comparator 52. This occurs when the speed of the highpressure compressor, as measured by an N pick-up 54, exceeds apredetermined level. Similarly, the main fuel bleed control circuit 50completes the connection to ground in response to output from anovertemperature comparator circuit 56. This occurs when thermocouples 58measure a temperature considered eX- cessive by the comparator. Thistemperature level is modified by means of manual switches 60 and 61which are set for particular operating conditions. When the stator vanepower control circuit 46 completes the connection to ground, the statorvane solenoid 38 is energized and serves to change the position of thevariable stator vanes 62 in the power turbine inlet and hence reduce thepower turbine speed. When the main fuel bleed control circuit 50completes the connection to ground, the main fuel bleed solenoid 42 isenergized to open the main fuel bleed valve 64 in the fuel supply systemso as to reduce the amount of fuel being delivered to the combustionchamber.

IGNITION AND STARTER POWER CONTROL UNIT The ignition and starter powercontrol unit is shown in FIGURE 2. It comprises two silicon controlledrectifiers Q1 and Q2 which operate as a flip-flop. The rectifier Q1controls the power applied to the relay 24 which in turn controls thestarter solenoid 16 and the ignition unit 18. Power is applied to theignition and starter power control unit 26 by the closing of switch S1.This supplies regulated D.C. voltage from the battery 12 to the voltageregulator 25 which serves to develop a regulated DC. voltage at thevarious terminals R throughout the system.

The silicon controlled rectifier Q1 is comprised of a cathode 68connected to ground, an anode 70 connected to the terminal R through adiode 727 and the windings of relay 24, and a control electrode 74connected to ground through a resistor 76. The silicon controlledrectifier Q2 is comprised of a cathode 77 connected to ground, an anode78 connected to the terminal R through a resistor 80, and a controlelectrode 82 connected to ground through a resistor 84. The anodes 70and 78 of controlled rectifiers Q1 and Q2 are interconnected by means ofa commutating capacitor 85.

The control electrode 82 of the rectifier Q2 is connected to theterminal R through a diode 86 and a capacitor 88, the junction of diode86 and capacitor 88 being connected to ground through a resistor 90. Thecontrol electrode 74 of rectifier Q1 is connected to a start-stopterminal T1 through a capacitor 92 and a diode 94, capacitor 96, and aresistor 98. One side of the capacitor 96, is connected to groundthrough a resistor 100, while the other side is connected to groundthrough a resistor 102. The junction of capacitor 92 and diode 94 is connected to the anode 78 of rectifier Q2 through a resistor 104.

When the master power switch S1 is closed, unregulated power is coupledthrough capacitor 88 and diode 86 to the control electrode 82. This willcause controlled rectifier Q2 to conduct and .assure that controlledrectifier Q1 is not conducting, having been commutated off by capacitor85. Setting the flip-flop up into this initial turn-on state will assurethe proper logic sequence preparation.

When the starting switch S3 is momentarily closed, the unregulated D.C.supply is connected to the terminal T1 and a pulse is applied to thecontrol electrode 74 of rectifier Q1 through the resistor 98, capacitor96, diode 94, and capacitor 92. It will be noted that a diode 103 isconnected to the anode 70 of rectifier Q1 through a resistor 106;however, current flow through the diode 103, resulting from a voltageapplied at T1, is blocked because of the high voltage at the anode 70when it is not conducting which supplies a back voltage to diode 103preventing it from conducting. However, the pulse applied to the controlelectrode 74 turns on rectifier Q1, energizing coil 24 and alsoconnecting the commutating capacitor to ground and across the rectifierQ2. This serves to cut off rectifier Q2.

The rectifier Q2 will stay off and the rectifier Q1 will stay on untilanother pulse is applied to the control electrode 82 of rectifier Q2.This pulse can be applied manually by a second closing of the momentarystart switch S3 which applies a second pulse to the terminal T1. Asecond pulse will flow. through the resistor 98 and capacitor 96. Itwill be blocked from flowing through the diode 94 since it is connectedto the high voltage at anode 78 of the nonconducting rectifier Q2.However, current can now flow through the diode 103, then through acapacitor 108 and a diode 110 also connected to the control electrode 82of rectifier Q2. This pulse serves to start the conduction of rectifierQ2. This conduction connects commutating capacitor 85 to ground acrossthe rectifier Q1, and shuts Q1 off, de-energizing coil 24.

The rectifier Q2 can also be turned on by a pulse applied through adiode 112 supplied with a pulse at terminal T2 from the N comparator 30or through a diode 114 supplied with a pulse at terminal T3 from thedelay timer 32.

When the rectifier Q2 is first turned off, by application of the firststart pulse through the closure of S3, the voltage developed at itsanode 78 is applied to the delay timer 32 via terminal T4 and line 35 tostart the timing cycle. At the end of a predetermined time delay, thedelay timer 32 provides the pulse to the diode 114 necessary to againstart the conduction of rectifier Q2 which will dc-energize coil 24 andabort the start attempt.

STATOR VANE AND MAIN FUEL BLEED SOLENOID CONTROL CIRCUITS The statorvane control circuit 46 and the main fuel bleed control circuit 50 areidentical, the one serving to complete the circuit from the main fuelbleed solenoid to ground and the other serving to complete the circuitof the stator vane solenoid 38 to ground. The circuit for performingthese functions is shown in FIGURE 3.

Each circuit has two input terminals T4 and T5. The terminal T4represents the connection from either the stator vane solenoid 38 (atline 44) or the main fuel bleed solenoid 42 (at line 48), depending onwhether the circuit is used for completing the connection of. the statorvane solenoid 38 to ground or for completing the connection of the mainfuel bleed solenoid 42 to ground. Similarly,

the input terminal T5 represents either the connection from the Ncomparator 52 or the overtemperature comparator 56. The outputs from theN comparator 52 and the overtemperature comparator 56 comprisecontinuous trains of pulses which are developed during either anoverspeed or an overternperature condition.

Each circuit 46 and 50 comprises a silicon controlled rectifier Q3having a cathode 120 connected to ground, an anode 122 connected to theterminal T4, and a control electrode 124 connected to ground through aresistor 126. The train of pulses at terminal T5 is connected to thecontrol electrode 124 through a diode 128. The train of pulses rendersthe rectifier Q3 conductive and thereby completes the connection of theterminal T4 to ground. The grounding of terminal T4 completes theenergization circuit of the stator vane solenoid or the main fuel bleedsolenoid, as the case may be.

The train of input pulses applied at terminal T5 is also connectedthrough a resistor 130 to the base 132 of a transistor Q4 having agrounded emitter 134 and a collector 136 connected to the regulatedvoltage terminal R through resistors 138 and 140. A timing capacitor 142is connected across the collector 136 and the emitter 134. So long as atrain of input pulses is applied to the base 132 of transistor Q4,transistor Q4 is maintained in a state of current conduction at eachinput pulse and this prevents the build up of a steady state voltage onthe capacitor 142. However, when the train of pulses terminates, thetransistor Q4 stops conducting and the voltage applied from theregulated supply at terminal R begins to build up on the capacitor 142.

The voltage charge developed across capacitor 142 is applied to the baseelectrode 144 of a unijunction transistor Q5, the base two electrode 146being connected to the regulated voltage terminal R through a resistor148, the base one electrode 150 being connected to ground through aresistor 152. When the charge on the capacitor 142 reaches the peakpoint voltage level necessary to fire the unijunction transistor Q5, thecurrent then flows through transistor Q5 and through a capacitor 154into the control electrode 158 of rectifier Q6.

The resistor 156 is connected between the control electrode 158 and thecathode 160 of a silicon controlled rectifier Q6, the anode 162 beingconnected to the terminal R through resistor 140. The voltage developedacross the resistor 156 causes the silicon controlled rectifier Q6 toconduct, thereby eifectively connecting its anode 160 to ground. It willbe noted that the anode 162 of silicon controlled rectifier Q6 isconnected to the anode 122 of rectifier Q3 through a capacitor 164. Thegrounding of the anode 162 discharges the capacitor 164 across the anodeand cathode of the rectifier Q3, shutting Q3 ofif.

Thus, a train of pulses applied at T5 turns on the rectifier Q3 andenergizes the associated load. The discontinuance of the train of pulsescauses the timing capacitor 142 to charge, turning transistor Q5 on, andcausing rectifier Q6 to conduct. Conduction of rectifier Q6 dischargesthe capacitor 164, shutting off rectifier Q3. The circuit will stay inthis condition until a succeeding train of pulses is applied at T5.

OTHER COMPONENTS The remaining circuits and components are conventionaland need not be described in detail. It suifices to point out that the Ncomparator 30, the N comparator 52, and the overtemperature comparator56 each generates a train of pulses when its respective input exceeds apredetermined level. The reference level of the overtemperaturecomparator 56 is alterable for various throttle lever positions by meansof manual switches 60 or 61 which are mounted on the throttle leverlinkage. These switches are used to insert or take out one or moreresistors from the comparator reference circuit to change the level atwhich an output is generated.

The delay timer 32 is also conventional and utilizes two unijunctiontransistors. Application of DC voltage from the ignition and starterpower control unit 26 through line 35 starts the charging of an RC.network. When the RC. network is charged, the unijunction transistorconducts, delivering an output pulse at line 33 aborting the startattempt.

Obviously the system is capable of various modifications andadaptations. In a practical case, the system was supplemented by variousadditional outputs which were used to energize warning devicesindicating an aborted starting attempt or an overspeed orovertemperature condition.

I claim:

1. In a system for automatically starting and controlling the operationof a gas turbine engine having a free power turbine, a compressorturbine and adjustable power turbine stator vanes, said system having alurality of accessories including a starter solenoid for con-trollingthe energization of a starter motor for rotating the compressor of saidengine during starting, an ignition unit for igniting the fuel flowinginto the combustion chamber of said engine during starting, anelectromagnetic fuel bleed valve actuator for controlling fuel flow tosaid combustion chamber, an electromagnetic stator vane actuator foradjusting the position of the power turbine stator vanes of said freepower turbine engine, a source of energization for said motor andaccessories, each of said accessories and said motor being in an initialenergization state wherein said starter motor and ignition unit arede-energized, said bleed valve is closed and said stator vanes arepositioned for maximum power turbine speed, the combination comprismg:

first switch means for establishing connections between said source andsaid starter solenoid and said ignition unit, respectively;

first means controlling said first switch means to change the state ofenergization of said starter solenoid and ignition unit to a secondstate whereby said starter motor and ignition unit are energized;

means responsive to an engine operating parameter for generating a firstcontrol voltage;

second means controlling said switch means, said second means beingresponsive to said first control voltage above a predetermined level forchanging the energization states of said ignition system and saidstarter solenoid to their respective initial energization states, saidlevel representng a successful start to said engine;

timer means responsive to a predetermined lapse of time for generating asecond control voltage, the occurrence of said second control voltageprior to the generation of said first control voltage controlling saidfirst switch means for changing the energization state of said startersolenoid and said ignition system to their respective initialenergization states whereby an attempted engine start is aborted;

second and third switch means for estbablishing connections between saidsource and said stator vane actuator and said fuel bleed solenoid,respectively; means responsive to the speed of rotation of said powerturbine for generating a third control voltage;

third means controlling said second switch means, said third means beingresponsive to said third control voltage above a predetermned level,said level representing an overspeed condition of said power turbine forchanging the energization state of said stator vane actuator foradjusting said stat-or vanes to reduce the speed of rotation of saidpower turbine;

means responsive to a predetermined measured gas temperature forgenerating a fourth control voltage; and fourth means controlling saidthird switch means,

said fourth means being responsive to said fourth control voltage abovea predetermined level for changing the energization state of said fuelbleed solenoid whereby fuel is bled from said combustion chamber of saidengine to reduce the temperature of said gas, said level representing anovertemperature condition.

2. The invention as defined in claim 1 wherein said third meanscontrolling said second switch means and said fourth means controllingsaid third switch means each comprises:

a signal responsive electric conduction device having a first and secondconduction state, the presence or absence of a third or fourth controlvoltage determining the state of a respective device, said second andthird switch means being responsive to the state of a respective device.

3. The invention as defined in claim 2 wherein each of said second andthird switch means comprises a first silicon controlled rectifier havingan anode, a grounded cathode and a control electrode, said anode andcathode being connected in the energization path of a respectiveactuator, said actuators being energized when a respective rectifier isconductive, and wherein said third and fourth control means eachcomprises:

a transistor having a base, a grounded emitter and a collector connectedto a regulated voltage supply through a resistor;

a timing capacitor connected between said collector and ground;

a unijunction transistor having a first electrode connected to saidsupply, a second electrode connected to ground through an outputresistor, and a control electrode connected to said collector;

a second silicon controlled rectifier having a grounded cathode, ananode connected to said supply and a control electrode;

a commutating capacitor connected between the anodes of said first andsecond silicon controlled rectifiers;

a respective one of said third and fourth control voltages being appliedsimultaneously to the base of said transistor and to the controlelectrode of said first silicon controlled rectifier to render saidfirst rectifier conductive, said control voltages comprising a train ofpulses whereby said timing capacitor is maintained in a state ofconduction When said control voltages are applied to said base toprohibit the development of a charge on said capacitor, and whereby inthe absence of a control voltage a charge develops on said timingcapacitor after a period determined by the time constants in circuitwith said timing capacitor, a predetermined charge on said timingcapacitor causing said unijunction transistor to conduct and renderingsaid second rectifier conductive effectively connecting said commutatingcapacitor across the anode and cathode of said first rectifier to stopconduction of said first rectifier.

4. The invention as defined in claim 1 wherein said engine operatingparameter is compressor turbine speed, and wherein said gas temperatureis measured at the inlet to said power turbine.

5. The invention as defined in claim 1 wherein said first switch meansis a relay having energizable windings and first and second initiallyopen contacts, said first contacts serving when closed to complete theconnections from said source to said starter solenoid, said secondcontacts serving when closed to complete the connections from saidsource to said ignition unit;

a regulated voltage supply;

and a silicon controlled rectifier connected in series wih saidwindings, said regulated voltage supply being connected across saidrectifier and said windings, said silicon controlled rectifier beingrendered conductive by said first means, said silicon controlledrectifier being rendered non-conductive in response to said firstcontrol voltage above a predetermined level or in response to saidsecond control voltage, whichever occurs first.

6. The invention as defined in claim 1 wherein said first switch is arelay having energizable windings and first and second initially opencontacts;

a regulated voltage supply;

first and second silicon controlled rectifiers, each of said rectifiershaving a grounded cathode, an anode, and a control electrode, the anodeof said first rectifier being connected to said regulated voltage supplythrough said windings, the anode of said second rectifier beingconnected to said regulated voltage pp y;

a commutating capacitor connected between said anodes, said first meanscomprising a manually operated switch for connecting said source througha capacitor to the control electrode of said first rectifier forrendering said first rectifier conductive and effectively connectingsaid commutating capacitor across the anode and cathode of said secondrectifier whereby said second rectifier is cut off;

said second means controlling said switch means comprising theconnection of said first control voltage to the control electrode ofsaid second rectifier to render said second rectifier conductive;

said timer means being initiated in response to the non-conduction ofsaid second rectifier, said second control voltage being applied to thecontrol electrode of said second rectifier to render said rectifierconductive at the end of said predetermined lapse of time;

the conduction of said second rectifier effectively connecting saidcommutating capacitor across the anode and cathode of said firstrectifier whereby said first rectifier is cut off.

References Cited UNITED STATES PATENTS 2,866,385 12/1958 Miller 6039.14XR 3,310,937 3/1967 Smith 6039.14 3,365,881 1/1968 McKenzie 60-39.14

CARLTON R. CROYLE, Primary Examiner ALLAN D. HERRMANN, AssistantExaminer US. Cl. X.R.

